In my U.S. Pat. No. 4,087,657 granted May 2, 1978, there were disclosed apparatus and method for synthesizing a ladder network of series inductors and shunt capacitors from the differential phase of the input impedance of a telephone transmission line. The frequencies of the poles and zeros of the ladder network corresponded to the maxima and minima of the differential phase characteristic. The values of the respective inductors and capacitors in the synthesized network are respectively proportional to the load inductances and the spacing therebetween in the actual transmission line. A microprocessor with an appropriate read-out device generates the load inductances and the spacings automatically in response to the impedance measurement. As a result relatively unskilled test personnel can quickly obtain data on loaded transmission lines.
In my copending patent application bearing the Ser. No. 62,773 and filed Aug. 1, 1979 now U.S. Pat. No. 4,229,626 granted Oct. 21, 1980 there is disclosed a structure for generating the derivative with respect to frequency of the phase angle of the complex input impedance of an unloaded cable pair over an extended frequency range from magnitude measurements only.
It is an object of this invention to combine the teachings of my two prior disclosures to reduce further the complexity of implementation as well as the skill and time required to identify the parameters of an inductively loaded telephone transmission loop.
It is a further object of this invention to simplify apparatus and method for testing inductively loaded telephone transmission loops in order to identify incorrect loading on such loops.